The invention relates generally to turbomachinery and, more specifically, to circumferential support arrangements for the airfoil portions of a row of blades or buckets mounted on a turbine rotor wheel.
Turbine blades or buckets are oftentimes supported at two locations along the radial length of the airfoil portion of the blades or buckets. Specifically, the radially-outer tips of the blades or buckets are engaged by individual tip shrouds while at locations intermediate the radially-inner and outer end of the airfoil portions, part-span or mid-span shrouds (sometimes referred to as mid-span snubbers) may be provided which engage similar mid-span shrouds on adjacent buckets.
Turbine bucket tip shrouds have a feature called a “hard face” which is the contact surface on each shroud that engages a similar contact surface or hard face on an adjacent shroud. The current tip shroud hard face design is a flat face which is oriented straight in a radial direction (see FIGS. 1 and 2). The tip shrouds support the buckets during turbine operation, holding them in proper alignment and resisting excessive movement due to the twisting forces exerted on the rotating buckets, while also acting as dampers of unwanted bucket vibrations. Some tip shrouds have well known Z-notch configurations where the hard faces or contact surfaces extend along adjacent multi-angled edges that often prove to be life-limiting locations for the buckets because they are subject to high stresses due to the bending of tip shroud overhangs and the load transfer between adjacent buckets. Shingling is another key problem with turbine bucket tip shrouds, caused by unequal displacement of pressure side and suction side overhangs of the tip shrouds.
Similarly, the mating hard faces or contact surfaces between adjacent mid-span shrouds or snubbers are also flat and oriented straight in a radial direction. Mid-span shrouds are particularly vulnerable to shingling and excessive vibrations, which also can be life-limiting.
It would therefore be desirable to provide a blade-to-blade interface at both tip shroud and mid-span shroud locations that reduce or eliminate the problems mentioned above with respect to stress, shingling and vibration.